Conveyor belts in which a plurality of metal links are arranged to present a substantially continuous supporting surface have been utilized for many years, particularly in association with furnaces wherein the conveyor belt constitutes a moving support for articles which are to be conveyed into and through the furnace for heat treatment purposes. The conveyor belt conventionally has a plurality of metal links arranged in plural rows which extend transversely of the belt, the links in adjacent rows being staggered to interfit with one another, and elongated connecting rods extend transversely of the belt for hingedly joining the links of adjacent rows. The metal links are cast from high alloy steels so as to withstand the high temperatures experienced in the heat treatment furnace, whereby the links are thus both difficult to cast and costly to manufacture. The pivot rods themselves are also often formed from high alloy steels, and are also costly.
In one conventional conveyor belt assembly of this general type, the metal links are generally of a cruciform shape and have hinge portions at opposite ends, whereby the hinge portions on the links of adjacent rows can be interleafed in substantially the same manner as a piano-type hinge, with an elongated hinge rod extending through the aligned interleafed hinge portions. With this type belt, the hinge rod functions not only to connect the links together, but also as a means for permitting the links to freely pivot and turn during belt movement. Since the hinge rods are the primary structure for connecting the links of adjacent rows together, the tension forces which are transmitted longitudinally of the belt are transmitted from the links of one row through the connecting rod to the links of the adjacent rows, and hence the rods are subjected to severe stresses. With conveyor belts of this type, it is necessary to make the rods of high alloy steels and of maximum cross-sectional diameter in order to withstand the stresses imposed thereon, and this hence makes such conveyor belts very costly to manufacture. In addition, the belts of this type have commonly experienced failure due to the hinge rods being distorted as a result of the substantial stresses imposed thereon, which failure often is referred to as "crank-shafting".
To avoid the problems and disadvantages associated with conveyor belts of the above type wherein the connecting rod is a highly loaded and stressed member, there is also known a conventional conveyor chain wherein the metal links themselves are provided with trunnions on one end which hingedly interfit within a hinge portion provided on the other end of an adjacent link so that the transfer of stresses along the chain occurs directly from link-to-link, whereby the connecting rods are provided solely as a means of retaining the hingedly connected links together. A chain of this general type is illustrated in U.S. Pat. No. 2 681 728 issued to F. J. Boron.
The metal link of the aforesaid Boron patent has a pair of hinge portions disposed at opposite ends of the link, which hinge portions are joined together by vertically spaced top and bottom plates which extend in substantially parallel relationships, with the region between said top and bottom plates being substantially open. The hinge portions at opposite ends of the link constitute only a partial cylindrical shape since the region disposed directly between the top and bottom plates is open. One of the hinge portions has a pair of sleevelike trunnions of reduced diameter associated therewith, which trunnions project outwardly from opposite sides of the hinge portions so as to hingedly interfit within the hinge portions associated with the other ends of the links of the next adjacent row, whereby the hingedly interfitting relationship of the trunnions into the hinge portions of the adjacent links provides a direct pivotal connection between the links of adjacent rows and also permits a direct force and load transfer therebetween. While a connecting rod does extend through the aligned hinge portions, nevertheless the intent of this rod is not as a load or stress transmitting member.
While the arrangement of the Boron patent, as described above, initially appears to possess desirable features, nevertheless experience with the Boron structure, and a more detailed analysis thereof, indicates that the Boron link possesses structural and functional problems which are disadvantageous. For example, due to the direct transfer of tension loads between the links of adjacent rows, the tension loads are imposed against the innermost sides of the trunnions, which loads are directed longitudinally outwardly so that the two trunnions are loaded in such manner that they tend to bend inwardly toward one another. Further, since the inner wall of the hinge portion is removed so as to open inwardly into the body of the link between the top and bottom plates, there is no strong structural member joined between the inner walls of the trunnions, and this thus creates a structural weakness which is believed to result in distorion and hence failure of the link due to the manner in which the trunnions are structurally coupled to the link. In addition, the Boron link has been observed to undesirably permit the articles being conveyed, specifically small articles, to become trapped between the upper and lower plates of the link body due to the substantial open space therebetween.
Due to the structural weakness in the aforementioned Boron link created by the opening between the trunnion-bearing hinge portion and the main link body, the Boron link was modified to eliminate this opening by forming the trunnion-bearing hinge portion as a solid sleeve. While this improved the strength of the link, nevertheless it has been observed that this modified Boron link experienced failure of a different type. More specifically, due to the very hostile environment in which conveyors of this type are used, the chain links are inevitably exposed to deposits, particularly carbon deposits. Further, with the increased usage of various types of high alloy steel, and the various types of heat treating and hardening processes, the conveyor belts are increasingly exposed to nickel and chrome oxides, and other types of precipitates. These deposits, oxides and precipitates, due to the clearance between the connecting rods and the hinge portions of the links, move into and fill up these clearance spaces such that, after several months of operation, the clearance space becomes completely filled with deposits such that the link hinge portion and the connecting rod effectively become swedged together and hence do not pivot with respect to one another, whereupon the rod then usually fails due to excessive torsional stress. In fact, not only have failures of this type been frequently observed, but it has been discovered that oftentimes the rods can not even be removed so as to permit replacement and repair of the links. This problem of collection of deposits has been a common problem with the modified Boron link inasmuch as the deposits enter into the space between the rod and the hinge portion of the link, which space can be accessed solely from the open ends of the trunnions, whereupon the deposits become trapped within the clearance space and thus ultimately create a swedging of the rod and link together. Further, with this modified Boron link, it is extremely difficult to oxidize the carbon deposits by exposure to oxygen since it is impossible to obtain full flow of oxygen into the clearance space, and hence oxidation of the carbon, due to the very limited access provided at the free ends of the trunnions.
This modified Boron link has hence experienced rather severe failures due to the entrapment of deposits, and the ultimate swedging of the links and rods together. Also, this modified link still has parallel upper and lower plates provided with an open space therebetween, which space permits small articles to be trapped therebetween.
There has also been developed a variation of the aforesaid modified Boron link, which variation is identical to the modified link except that the bottom plate is eliminated and replaced with a single platelike vertical rib fixed to and projecting downwardly from the top plate, which rib extends longitudinally of the link and integrally joins to the hinge portions adjacent the midpoints thereof. While this link eliminates the open space between the top and bottom plates associated with the modified Boron link, nevertheless this link variation results in the pocket between the ribs of sidewardly adjacent links being about three inches wide, whereas the tooth width on the conventional driving sprocket is only about one inch wide, so that the belt formed from these links experiences substantial sideward wandering relative to the sprocket wheels, which wandering is sufficient to often cause interference with the sidewalls of the chutes used for supplying the articles to or removing the articles from the conveyor belt.
Still further, this last-mentioned link variation has undesirably low strength when subjected to tensile stresses in the longitudinal direction of the chain, and in fact the link has been observed to pull apart when subject to a stress of about 19,000 psi. This link variation also has been observed to undergo substantial stretch or elongation under load such that, when a chain involving this link has been in use for about six months, oftentimes it has been observed that the chain has stretched up to eight inches, and hence the conveyor must be shut down so as to permit removal of several links to eliminate the undesirable slack. This link variation also has been observed to undergo stress failure at the sharp corner where the top plate merges with the hinge portions. Still further, this link variation utilizes hinge portions which are effectively closed in the same manner as in the modified Boron link, and thus this conveyor belt also experiences entrapment of deposits between the hinge portion and the connecting rod which ultimately result in swedging of the rod to the link, which in turn results in torsional failure of the rod.
Accordingly, the present invention relates to an improved metal link for a conveyor belt of the aforesaid type, which metal link significantly improves upon and, in some cases, effectively overcomes many of the disadvantages associated with the known trunnion-type metal links as described above.
More specifically, it is an object of the present invention to provide an improved conveyor belt of the type utilizing metal links and designed specifically for use with heat treatment furnaces, which conveyor belt is believed to significantly reduce the probability of belt failures of the type which have been long standing in this technology, and which have persisted even though numerous attempts have been made to overcome these failures.
A further object of this invention is to provide an improved conveyor belt, as aforesaid, employing an improved cast metal link of the trunnion type whereby the hinge portion associated with the trailing end of the link has outwardly projecting trunnions on both sides thereof and defines a smaller-diameter opening therethrough for the connecting rod, whereby the hinge portion at the leading end of the link has a larger-diameter opening therethrough for accommodating the trunnions, whereby the link has a main body formed as an elongated tube which extends longitudinally of the link and rigidly and integrally joins to the hinge portions, and whereby the pivotal body is hollow and the interior thereof communicates with the openings through the hinge portions to permit deposits within the hinge portions to move into the interior of the body to minimize collection of deposits between the hinge portions and the connecting rods to minimize swedging together of the rods and links.
A still further object of this invention is to provide an improved conveyor belt link, as aforesaid, which has substantially increased strength in relationship to the known links described above, which accomplishes this substantial increase in strength with only a minimal and hence negligible increase in weight, and which substantially minimizes or eliminates the problem of belt stretch which has been observed in many of the known belts.
Another object of this invention is to provide an improved belt link, as aforesaid, which, by provision of the substantially closed tubular body, prevents articles from being trapped or engaged with or between the links, which preserves the minimum width pockets between sidewardly adjacent links so as to more closely accommodate the sprocket wheel teeth and hence prevent sideward wandering of the belt, and which additionally has a small access opening in the bottom of the tubular body to permit oxygen or other gases to enter into the interior of the body and thence into the hinge portions when oxidation of the carbon deposits is desired so as to provide increased access to the deposits within the hinge portions of the links.
Still another object of the invention is to provide an improved conveyor belt link, as aforesaid, which incorporates an internal rib which extends circumferentially around the outer wall of the hinge portion associated with the front end of the link, namely that hinge portion which has the largest diameter opening therethrough, which rib is positionable in the space between the trunnions which project into the hinge portion from opposite ends thereof, whereby the rib significantly strengthens this hinge portion of the link so prevent stretching or weakening of the link due not only to the thinner section associated with this hinge portion, but due also to the wear which generally occurs on this hinge portion due to the sliding of same along skid tiles during the return movement of the belt along the lower belt reach.
In the conveyor belt of this invention, the improved metal link in its preferred embodiment includes an elongated tubular body which extends in a longitudinal direction of the link and has a hollow interior. This tubular body includes a substantially planar top wall and a pair of substantially parallel sidewalls projecting downwardly therefrom. The top wall has substantially planar wings which are continuous with the top wall and project outwardly beyond the sidewalls of the body to form an enlarged upper support surface. These wings result in the sidewardly adjacent links defining a substantially continuous support surface for articles. The body, at its forward end, defines a front hinge portion which is defined by an opening which extends transversely through the sidewalls of the body, which opening is defined by a substantially semi-cylindrical end wall which extends between and is substantially continuous with the top and bottom walls of the body. This end wall preferably has a strengthening rib which projects inwardly therefrom and around the circumference thereof substantially midway between the opposite ends of the opening. This opening also is in communication with the hollow interior of the body. A rear hinge portion is also formed at the other end of the tubular body and defines an opening which extends transversely of the body in substantially parallel relationship to the opening defined in the front hinge portion. The opening through the rear hinge portion is of smaller diameter than the opening in the front hinge portion. The opening in the rear hinge portion is again defined by a substantially semi-cylindrical wall which extends between and integrally joins the top and bottom walls of the tubular body, and the interior of this opening is in communication with the hollow interior of the body. The rear hinge portion includes a pair of substantially cylindrical trunnions which are aligned with the rear opening and project outwardly from opposite sides of the body so that the rear opening extends through the trunnions. The trunnions have an outer diameter which is slightly smaller than the diameter of the front opening so as to be positionable in the front openings of two adjacent similar links. Elongated connecting rods extend through the rear openings of links aligned in sidewardly extending rows to provide structural connection of the links, which links have the trunnions thereof structurally and pivotally supported within the front openings of the links in the next adjacent row.
Other objects and purposes of the invention will be apparent to persons familiar with conveyor belts of this general type upon reading the following specification and inspecting the accompanying drawings.